Milk Heating / Curd Cooking Requirements
Controlling milk temperature per recipe instructions can be a real problem for the occasional cheese maker. Not so much for the initial warming to the desired ripening temperature (which can easily be done in a sink of hot water). Maintaining temperature at the target over the ripening period can be a little more difficult, especially if the ambient temperature is low. Most challenging, however, is the step of slowly increasing curd and whey temperature over a set time when cooking or "scalding" the curds, as it's easy to get distracted and "miss your marks" or worse, over-cook and ruin your batch.
Time / Temperature Requirements
To cook curds consistently you need control two variables, time and temperature, simultaneously. To help visualize consider the temperature requirements for a typical cheddar. A chart of the time / temperature called for is shown below. The recipe calls for warming the millk to 88 deg. F (Interval 1), adding the cultures and maintaining 88 F during ripening for an hour (2). After rennet has been added and curds formed and cut (3), the directions are: "over low heat, slowly bring the curds to 102 deg. F over 40 min while stirring" (4), then to hold that temperature while stirring for 1 hour or so until the curds are ready to drain (5).
Think of this chart as a "typical" time / temperature chart in that most cooked-curd cheeses follow this pattern. For cooking curds, the most critical period is the red (4) interval because this is the most difficult to control.
The good news is that for most of the cheeses, you will make the rate of temperature increase during this interval fairly consistent. In the case of the above cheddar, the rate of temperature increase is .4 degrees per minute. Another (read easier) way of stating this is that the recipe calls for an increased rate of 2.5 min. per degree.
While other recipes will call for slightly different rates, the majority will be close to this 2.5 number. The implication here is that once you have a system that is "tuned" for this range, the same system should be able to handle most of the other types of cheeses.